Amazonian Tree Mortality during the 1997 El Niño Drought

Abstract: In 1997, the Amazon Basin experienced an exceptionally severe El Niño drought. We assessed effects of this rare event on mortality rates of trees in intact rain forest based on data from permanent plots. Long-term (5- to 13-year) mortality rates averaged only 1.12% per year prior to the drought. During the drought year, annual mortality jumped to 1.91% but abruptly fell back to 1.23% in the year following El Niño. Trees dying during the drought did not differ significantly in size or species composition from those that died previously, and there was no detectable effect of soil texture on mortality rates. These results suggest that intact Amazonian rainforests are relatively resistant to severe El Niño events.     

Solvent toxicity to amphibian embryos and larvae

Organic micropollutants are often damaging for aquatic organisms. Being usually hydrophobic compounds, they are often dissolved in an organic co-solvent which increases their solubility in water. The aim of this study was to study the toxicity of various solvents on embryos (protected or not by jelly coat) and on tadpoles of the common frog (Rana temporaria). Tested solvents were methanol (MeOH), methylene chloride (CH(2)Cl(2)), dimethyl sulfoxyde (DMSO), acetone (Ac) and ethanol (EtOH). Embryos exhibited higher mortality rates than tadpoles. Embryos with jelly were more sensitive to high concentration of solvents than embryos without jelly (except for acetone). According to these results, Ac, DMSO and CH(2)Cl(2) can be used as co-solvents in water to help the dissolution of micropollutants at concentration equal to or lower than 0.001 ml/l for frog embryos, and EtOH, Ac and CH(2)Cl(2) at concentration equal to or lower than 0.01 ml/l for Rana temporaria tadpoles.     

Sampling and analytical methodology development for the determination of primary and secondary low molecular weight amines in ambient air

In this project, a sampling device and an analytical method have been developed to simultaneously analyse the most frequently found low molecular weight amines, including aliphatic, aromatic and alcohol amines. These amines are diethanolamine, ethanolamine, methylamine, isopropylamine, morpholine, dimethylamine, and aniline. A sampling device was developed using a 37 mm cassette with glass fibre filters impregnated with sulfuric acid. Immediately after sampling, the filter was transferred to vials containing a solution of dansyl chloride. Dansyl chloride was used for derivatisation because it forms aromatic sulfonamides that are fluorescent and easy to protonate for MS detection. The effect of using an internal standard made with the dansylated derivative of 1-(2-methoxyphenyl)piperazine (MOPIP) on the uncertainty and efficiency of the method was also evaluated. This internal standard was spiked directly onto filters. The coupling of HPLC/ESI-MS was used for the simultaneous analysis of all the derivatives. This method showed detection limits of about 0.03 microg mL(-1) to 0.3 microg mL(-1) of amine with an average expanded uncertainty of 3% to 6% depending on the amine. The methodology recoveries are close to 100% for all the amines, and the overall estimated expanded uncertainties vary between 10% and 13% depending on the amine. This new strategy will be useful in evaluating workplace air since a unique sampling system will be used, independent of the amine to be quantified.     

THE ENHANCED ROLE OF WATER CONSERVATION IN THE COST-BENEFIT ANALYSIS OF WATER PROJECTS1

The concept of water conservation has increased in importance because of revisions in the rules and procedures for performing cost-benefit analyses of federal water projects. These revisions include a requirement that nonstructural and water conservation measures be incorporated into economic assessments of projects. Project analyses will now proceed as if water supplies were allocated “most effectively,” that is, to their highest valued uses. A related requirement provides that the net benefits of any project should now be valued using willingness to pay measures. A specific cost-benefit methodology accommodating the revisions is constructed and discussed. Informational requirements for applying this methodology are identified. In addition to being consistent with federal mandates, this technique offers important advantages over the traditional “requirements” approach to water supply planning.     

A statistical approach to field measurements of the chemical evolution of cold (<0°C) snow cover

Two statistical methods for the analysis of data on the evolution of the chemical composition of cold snow (<0°C) in the field (Lac Laflamme, Quebec) were compared. The methods used on the data were regression analysis (One sample per sampling date over a long cold period) and ANOVA (replicate samples on a restricted number of sampling dates over shorter periods). The relative power of the tests to determine the detectable amplitude of chemical changes was derived from the theoretical power of the tests under comparable conditions of sampling (number of observations) and from the estimated error variances of the measured data.The results of the study on the evolution of sulfates (SO₄) concentrations in discretely identified snow strate clearly showed that for six of the eight strata, significant losses of SO₄ occurred in snow during cold periods. The relative amplitude of the significant losses varied between 1% per day and 4% per day depending on the initial concentrations in the snow and the prevailing meteorological conditions.The analysis of the data also demonstrated that for the same number of samples, the regression analysis is more efficient in detecting the chemical changes in snow than the alternative ANOVA method. The use of this information to plan sampling programs of cold snow under both field and laboratory conditions is discussed.     

Glacial-interglacial changes in the occurrence of Pb, Cd, Cu and Zn in Vostok Antarctic ice from 240 000 to 410 000 years BP

Lead (Pb), cadmium (Cd), copper (Cu) and zinc (Zn) have been measured by electrothermal atomic absorption spectrometry in various sections of the 3623 m deep ice core drilled at Vostok, in central East Antarctica. The sections were dated from 240 to 410 kyear BP (Marine Isotopic Stages (MIS) 7.5 to 11.3), which corresponds to the 3rd and 4th glacial-interglacial cycles before present. Concentrations are found to have varied greatly during this 170 kyear time period, with high concentration values during the coldest climatic stages such as MIS 8.4 and 10.2 and much lower concentration values during warmer periods, such as the interglacials MIS 7.5, 9.3 and 11.3. Rock and soil dust were the dominant sources for Pb, whatever the period, and for Zn and Cu and possibly Cd during cold climatic stages. The contribution from volcanic emissions was important for Cd during all periods and might have been significant for Cu and Zn during warm periods.